1. Field of the Invention
The present invention relates to an actuator used with an optical pickup, and more particularly, to an actuator used with an optical pickup using plate coils.
2. Description of the Related Art
In general, optical pickups record information by irradiating light toward a disc as a recording medium through an objective lens, or reproduce information by receiving light that is reflected from the disc. Optical pickups include an actuator which adjusts the position of the objective lens such that light is irradiated to a precise position of the disc.
FIG. 1 illustrates the structure of a conventional actuator used with an optical pickup. Referring to FIG. 1, the actuator used with an optical pickup includes a blade 2 on which an objective lens 1 is mounted, a plurality of wires 7 which support the blade 2 in order to enable the blade 2 to move toward a holder 3, a pair of magnets 5 which are installed on a base 4 as an electromagnetic drive unit which drives the blade 2 in a focusing direction Z and a tracking direction X and adjusts the position of the objective lens 1, and a plate coil 6 which is installed on the blade 2 to be arranged between the pair of magnets 5.
As illustrated in FIG. 2, a plurality of pattern coils 6a and 6b are formed in the plate coil 6. Thus, if current flows through the plurality of pattern coils 6a and 6b, an electromagnetic force caused by interaction with the magnets 5 is generated, and thus the blade 2 is driven. Reference numerals 6a and 6b denote a focusing coil and a tracking coil, respectively. In the prior art, a winding coil wound in a predetermined position of the blade 2 instead of the plate coils 6a and 6b may be employed, but the plate coil 6 is preferred to reduce the size of optical pickups.
As illustrated in FIGS. 2 and 3, one side of each magnet 5 is polarized into several portions. Since the pattern coils 6a and 6b to focus and track are placed on one plane due to the structural characteristics of the plate coil 6, each magnet 5 is formed in a polarized structure as in FIGS. 2 and 3, so as to form magnetic force lines corresponding to each of the pattern coils 6a and 6b. 
If one side of each magnet 5 is polarized into several portions, a magnetized gap G exists between the poles of each of the magnets 5. The magnetized gap G generally has the width W of about 0.2-1.2 mm. However, since the size of a slim type magnet is only 3.5-4 mm while the size of a half-height type magnet is only 5-7 mm, the width W of the magnetized gap G cannot be ignored. In particular, as illustrated in FIGS. 2 and 3, in a structure where the magnetized gap G is formed in three places in a horizontal direction and in two places in a vertical direction, the sum of the width W of the magnetized gap G affects more of the area of each of the magnets 5. Furthermore, if polarization becomes more active, the effective magnet area required to generate an electromagnetic force is reduced, and thus sensitivity is lowered.
Thus, actuators used with optical pickups which can minimize the amount of polarization of a magnet and prevent a decrease in actuator sensitivity are necessary.